Investigation of Spring Irrigation and Tillage to Control Overwintering Chilo suppressalis (Walker)

Overwintering larvae and pupae are the most important source of first generation of Chilo suppressalis (Walker) in early spring. Aging larvae and pupae harbor strong stress-tolerance and also potential pesticide resistance. Therefore, at present, irrigation and tillage are mainly used for killing the first generation of C. suppressalis. However, the efficiency of this method was not clear. To study the exact efficiency, overwintering larvae and pupae were collected from rice straw in field. And they were placed in water to test their tolerance to immersion indoor. The control effect of irrigation and tillage was tested in field and repeated in different years. As a result, in tolerance experiment, the mortality of aging larvae was less than 50% on day 8 and reached 80% on day 12. The mortality of pupae reached 75% within 72 hours. In the field, the escape rate of larvae was the highest on day 1 (4.49%), after which time it gradually decreased. The cumulative escape rate was 7.89% within 4 days. When the fields were tilled immediately after immersion, the cumulative escape rate decreased to 1.05%. There was no significant difference in escape rate with different tillage depths. This is the first study to systematically investigate the control effect of irrigation and tillage on overwintering C. suppressalis. And the results showed that aging larvae of C. suppressalis had strong tolerance to immersion. But the tolerance of pupa to water was relatively weak. Tillage could effectively reduce the escape rate of aging larvae. So, “Tilling immediately after irrigation” was recommended in early spring. This will provide guidance for agricultural control of C. suppressalis